org.elasticsearch.index.engine.LiveVersionMap Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of elasticsearch Show documentation
Show all versions of elasticsearch Show documentation
Elasticsearch subproject :server
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch licenses this file to you under
* the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.elasticsearch.index.engine;
import org.apache.lucene.search.ReferenceManager;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.RamUsageEstimator;
import org.elasticsearch.common.lease.Releasable;
import org.elasticsearch.common.util.concurrent.ConcurrentCollections;
import org.elasticsearch.common.util.concurrent.KeyedLock;
import java.io.IOException;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.atomic.AtomicLong;
/** Maps _uid value to its version information. */
final class LiveVersionMap implements ReferenceManager.RefreshListener, Accountable {
private final KeyedLock keyedLock = new KeyedLock<>();
private static final class VersionLookup {
private static final VersionLookup EMPTY = new VersionLookup(Collections.emptyMap());
private final Map map;
// each version map has a notion of safe / unsafe which allows us to apply certain optimization in the auto-generated ID usecase
// where we know that documents can't have any duplicates so we can skip the version map entirely. This reduces
// the memory pressure significantly for this use-case where we often get a massive amount of small document (metrics).
// if the version map is in safeAccess mode we track all version in the version map. yet if a document comes in that needs
// safe access but we are not in this mode we force a refresh and make the map as safe access required. All subsequent ops will
// respect that and fill the version map. The nice part here is that we are only really requiring this for a single ID and since
// we hold the ID lock in the engine while we do all this it's safe to do it globally unlocked.
// NOTE: these values can both be non-volatile since it's ok to read a stale value per doc ID. We serialize changes in the engine
// that will prevent concurrent updates to the same document ID and therefore we can rely on the happens-before guanratee of the
// map reference itself.
private boolean unsafe;
private VersionLookup(Map map) {
this.map = map;
}
VersionValue get(BytesRef key) {
return map.get(key);
}
VersionValue put(BytesRef key, VersionValue value) {
return map.put(key, value);
}
boolean isEmpty() {
return map.isEmpty();
}
int size() {
return map.size();
}
boolean isUnsafe() {
return unsafe;
}
void markAsUnsafe() {
unsafe = true;
}
}
private static final class Maps {
// All writes (adds and deletes) go into here:
final VersionLookup current;
// Used while refresh is running, and to hold adds/deletes until refresh finishes. We read from both current and old on lookup:
final VersionLookup old;
// this is not volatile since we don't need to maintain a happens before relation ship across doc IDs so it's enough to
// have the volatile read of the Maps reference to make it visible even across threads.
boolean needsSafeAccess;
final boolean previousMapsNeededSafeAccess;
Maps(VersionLookup current, VersionLookup old, boolean previousMapsNeededSafeAccess) {
this.current = current;
this.old = old;
this.previousMapsNeededSafeAccess = previousMapsNeededSafeAccess;
}
Maps() {
this(new VersionLookup(ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency()), VersionLookup.EMPTY, false);
}
boolean isSafeAccessMode() {
return needsSafeAccess || previousMapsNeededSafeAccess;
}
boolean shouldInheritSafeAccess() {
final boolean mapHasNotSeenAnyOperations = current.isEmpty() && current.isUnsafe() == false;
return needsSafeAccess
// we haven't seen any ops and map before needed it so we maintain it
|| (mapHasNotSeenAnyOperations && previousMapsNeededSafeAccess);
}
/**
* Builds a new map for the refresh transition this should be called in beforeRefresh()
*/
Maps buildTransitionMap() {
return new Maps(new VersionLookup(ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency(current.size())),
current, shouldInheritSafeAccess());
}
/**
* builds a new map that invalidates the old map but maintains the current. This should be called in afterRefresh()
*/
Maps invalidateOldMap() {
return new Maps(current, VersionLookup.EMPTY, previousMapsNeededSafeAccess);
}
}
// All deletes also go here, and delete "tombstones" are retained after refresh:
private final Map tombstones = ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency();
private volatile Maps maps = new Maps();
// we maintain a second map that only receives the updates that we skip on the actual map (unsafe ops)
// this map is only maintained if assertions are enabled
private volatile Maps unsafeKeysMap = new Maps();
/**
* Bytes consumed for each BytesRef UID:
* In this base value, we account for the {@link BytesRef} object itself as
* well as the header of the byte[] array it holds, and some lost bytes due
* to object alignment. So consumers of this constant just have to add the
* length of the byte[] (assuming it is not shared between multiple
* instances).
*/
private static final long BASE_BYTES_PER_BYTESREF =
// shallow memory usage of the BytesRef object
RamUsageEstimator.shallowSizeOfInstance(BytesRef.class) +
// header of the byte[] array
RamUsageEstimator.NUM_BYTES_ARRAY_HEADER +
// with an alignment size (-XX:ObjectAlignmentInBytes) of 8 (default),
// there could be between 0 and 7 lost bytes, so we account for 3
// lost bytes on average
3;
/**
* Bytes used by having CHM point to a key/value.
*/
private static final long BASE_BYTES_PER_CHM_ENTRY;
static {
// use the same impl as the Maps does
Map map = ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency();
map.put(0, 0);
long chmEntryShallowSize = RamUsageEstimator.shallowSizeOf(map.entrySet().iterator().next());
// assume a load factor of 50%
// for each entry, we need two object refs, one for the entry itself
// and one for the free space that is due to the fact hash tables can
// not be fully loaded
BASE_BYTES_PER_CHM_ENTRY = chmEntryShallowSize + 2 * RamUsageEstimator.NUM_BYTES_OBJECT_REF;
}
/**
* Tracks bytes used by current map, i.e. what is freed on refresh. For deletes, which are also added to tombstones, we only account
* for the CHM entry here, and account for BytesRef/VersionValue against the tombstones, since refresh would not clear this RAM.
*/
final AtomicLong ramBytesUsedCurrent = new AtomicLong();
/**
* Tracks bytes used by tombstones (deletes)
*/
final AtomicLong ramBytesUsedTombstones = new AtomicLong();
@Override
public void beforeRefresh() throws IOException {
// Start sending all updates after this point to the new
// map. While reopen is running, any lookup will first
// try this new map, then fallback to old, then to the
// current searcher:
maps = maps.buildTransitionMap();
assert (unsafeKeysMap = unsafeKeysMap.buildTransitionMap()) != null;
// This is not 100% correct, since concurrent indexing ops can change these counters in between our execution of the previous
// line and this one, but that should be minor, and the error won't accumulate over time:
ramBytesUsedCurrent.set(0);
}
@Override
public void afterRefresh(boolean didRefresh) throws IOException {
// We can now drop old because these operations are now visible via the newly opened searcher. Even if didRefresh is false, which
// means Lucene did not actually open a new reader because it detected no changes, it's possible old has some entries in it, which
// is fine: it means they were actually already included in the previously opened reader, so we can still safely drop them in that
// case. This is because we assign new maps (in beforeRefresh) slightly before Lucene actually flushes any segments for the
// reopen, and so any concurrent indexing requests can still sneak in a few additions to that current map that are in fact reflected
// in the previous reader. We don't touch tombstones here: they expire on their own index.gc_deletes timeframe:
maps = maps.invalidateOldMap();
assert (unsafeKeysMap = unsafeKeysMap.invalidateOldMap()) != null;
}
/**
* Returns the live version (add or delete) for this uid.
*/
VersionValue getUnderLock(final BytesRef uid) {
return getUnderLock(uid, maps);
}
private VersionValue getUnderLock(final BytesRef uid, Maps currentMaps) {
assert keyedLock.isHeldByCurrentThread(uid);
// First try to get the "live" value:
VersionValue value = currentMaps.current.get(uid);
if (value != null) {
return value;
}
value = currentMaps.old.get(uid);
if (value != null) {
return value;
}
return tombstones.get(uid);
}
VersionValue getVersionForAssert(final BytesRef uid) {
VersionValue value = getUnderLock(uid, maps);
if (value == null) {
value = getUnderLock(uid, unsafeKeysMap);
}
return value;
}
boolean isUnsafe() {
return maps.current.isUnsafe() || maps.old.isUnsafe();
}
void enforceSafeAccess() {
maps.needsSafeAccess = true;
}
boolean isSafeAccessRequired() {
return maps.isSafeAccessMode();
}
/**
* Adds this uid/version to the pending adds map iff the map needs safe access.
*/
void maybePutUnderLock(BytesRef uid, VersionValue version) {
assert keyedLock.isHeldByCurrentThread(uid);
Maps maps = this.maps;
if (maps.isSafeAccessMode()) {
putUnderLock(uid, version, maps);
} else {
maps.current.markAsUnsafe();
assert putAssertionMap(uid, version);
}
}
private boolean putAssertionMap(BytesRef uid, VersionValue version) {
putUnderLock(uid, version, unsafeKeysMap);
return true;
}
/**
* Adds this uid/version to the pending adds map.
*/
void putUnderLock(BytesRef uid, VersionValue version) {
Maps maps = this.maps;
putUnderLock(uid, version, maps);
}
/**
* Adds this uid/version to the pending adds map.
*/
private void putUnderLock(BytesRef uid, VersionValue version, Maps maps) {
assert keyedLock.isHeldByCurrentThread(uid);
assert uid.bytes.length == uid.length : "Oversized _uid! UID length: " + uid.length + ", bytes length: " + uid.bytes.length;
long uidRAMBytesUsed = BASE_BYTES_PER_BYTESREF + uid.bytes.length;
final VersionValue prev = maps.current.put(uid, version);
if (prev != null) {
// Deduct RAM for the version we just replaced:
long prevBytes = BASE_BYTES_PER_CHM_ENTRY;
if (prev.isDelete() == false) {
prevBytes += prev.ramBytesUsed() + uidRAMBytesUsed;
}
ramBytesUsedCurrent.addAndGet(-prevBytes);
}
// Add RAM for the new version:
long newBytes = BASE_BYTES_PER_CHM_ENTRY;
if (version.isDelete() == false) {
newBytes += version.ramBytesUsed() + uidRAMBytesUsed;
}
ramBytesUsedCurrent.addAndGet(newBytes);
final VersionValue prevTombstone;
if (version.isDelete()) {
// Also enroll the delete into tombstones, and account for its RAM too:
prevTombstone = tombstones.put(uid, (DeleteVersionValue) version);
// We initially account for BytesRef/VersionValue RAM for a delete against the tombstones, because this RAM will not be freed up
// on refresh. Later, in removeTombstoneUnderLock, if we clear the tombstone entry but the delete remains in current, we shift
// the accounting to current:
ramBytesUsedTombstones.addAndGet(BASE_BYTES_PER_CHM_ENTRY + version.ramBytesUsed() + uidRAMBytesUsed);
if (prevTombstone == null && prev != null && prev.isDelete()) {
// If prev was a delete that had already been removed from tombstones, then current was already accounting for the
// BytesRef/VersionValue RAM, so we now deduct that as well:
ramBytesUsedCurrent.addAndGet(-(prev.ramBytesUsed() + uidRAMBytesUsed));
}
} else {
// UID came back to life so we remove the tombstone:
prevTombstone = tombstones.remove(uid);
}
// Deduct tombstones bytes used for the version we just removed or replaced:
if (prevTombstone != null) {
long v = ramBytesUsedTombstones.addAndGet(-(BASE_BYTES_PER_CHM_ENTRY + prevTombstone.ramBytesUsed() + uidRAMBytesUsed));
assert v >= 0 : "bytes=" + v;
}
}
/**
* Removes this uid from the pending deletes map.
*/
void removeTombstoneUnderLock(BytesRef uid) {
assert keyedLock.isHeldByCurrentThread(uid);
long uidRAMBytesUsed = BASE_BYTES_PER_BYTESREF + uid.bytes.length;
final VersionValue prev = tombstones.remove(uid);
if (prev != null) {
assert prev.isDelete();
long v = ramBytesUsedTombstones.addAndGet(-(BASE_BYTES_PER_CHM_ENTRY + prev.ramBytesUsed() + uidRAMBytesUsed));
assert v >= 0 : "bytes=" + v;
}
final VersionValue curVersion = maps.current.get(uid);
if (curVersion != null && curVersion.isDelete()) {
// We now shift accounting of the BytesRef from tombstones to current, because a refresh would clear this RAM. This should be
// uncommon, because with the default refresh=1s and gc_deletes=60s, deletes should be cleared from current long before we drop
// them from tombstones:
ramBytesUsedCurrent.addAndGet(curVersion.ramBytesUsed() + uidRAMBytesUsed);
}
}
/**
* Caller has a lock, so that this uid will not be concurrently added/deleted by another thread.
*/
DeleteVersionValue getTombstoneUnderLock(BytesRef uid) {
assert keyedLock.isHeldByCurrentThread(uid);
return tombstones.get(uid);
}
/**
* Iterates over all deleted versions, including new ones (not yet exposed via reader) and old ones (exposed via reader but not yet GC'd).
*/
Iterable> getAllTombstones() {
return tombstones.entrySet();
}
/**
* clears all tombstones ops
*/
void clearTombstones() {
tombstones.clear();
}
/**
* Called when this index is closed.
*/
synchronized void clear() {
maps = new Maps();
tombstones.clear();
ramBytesUsedCurrent.set(0);
// NOTE: we can't zero this here, because a refresh thread could be calling InternalEngine.pruneDeletedTombstones at the same time,
// and this will lead to an assert trip. Presumably it's fine if our ramBytesUsedTombstones is non-zero after clear since the index
// is being closed:
//ramBytesUsedTombstones.set(0);
}
@Override
public long ramBytesUsed() {
return ramBytesUsedCurrent.get() + ramBytesUsedTombstones.get();
}
/**
* Returns how much RAM would be freed up by refreshing. This is {@link #ramBytesUsed} except does not include tombstones because they
* don't clear on refresh.
*/
long ramBytesUsedForRefresh() {
return ramBytesUsedCurrent.get();
}
@Override
public Collection getChildResources() {
// TODO: useful to break down RAM usage here?
return Collections.emptyList();
}
/**
* Returns the current internal versions as a point in time snapshot
*/
Map getAllCurrent() {
return maps.current.map;
}
/**
* Acquires a releaseable lock for the given uId. All *UnderLock methods require
* this lock to be hold by the caller otherwise the visibility guarantees of this version
* map are broken. We assert on this lock to be hold when calling these methods.
* @see KeyedLock
*/
Releasable acquireLock(BytesRef uid) {
return keyedLock.acquire(uid);
}
}